Chemistry - C6 - Organic Chemistry

organic chemistry refers to compounds containing which element?

carbon

what is a hydrocarbon?

a compound containing only carbon and hydrogen atoms

name the first four alkanes

1. methane (CH₄)

2. ethane (C₂H₆)

3. propane (C₃H₈)

4. butane (C₄H₁₀)

what is the name for CH₄

methane

what is the chemical formula for ethane?

C₂H₆

how many carbon atoms are in a molecule of propane?

3

what is the name of the alkane with four carbon atoms?

butane (C₄H₁₀)

what is the name for a compound with no double bonds?

a saturated compound

• all alkanes are saturated compounds

what is the general formula for an alkane?

C_nH_2n+2

what do properties of hydrocarbons depend on?

the length of their carbon chain

for alkanes, what happens to boiling points as length of chains increase?

boiling points increase

• the first four alkanes are gas at room temp due to their low boiling point

shorter alkanes are more (…) than longer alkanes

• name three possible answers

• lower boiling points

• more volatile (evaporate more easily)

• more flammable

  • therefore better fuels

as the chain length of alkanes increases, do they become more or less viscous, volatile and flammable?

• more viscous

• less volatile

• less flammable

what is the main use of hydrocarbons and why?

for fuel

• because they release lots of energy when burnt with oxygen

as long as there is sufficient oxygen when burning a hydrocarbon, what occurs?

complete combustion

• hydrocarbon + oxygen → carbon dioxide + water

is combustion an exothermic or endothermic reaction?

exothermic

what is oxidised during complete combustion?

hydrogen and carbon

• creating water

what is a homologous series?

a group of chemicals which have similar chemical properties and can be represented by a general formula

what is the functional group in an alcohol?

-OH

what is the general formula for alcohols?

C_nH_2n+1OH

are alcohols hydrocarbons?

no

• they contain oxygen

what are the first four alcohols?

1. methanol (CH₃OH)

2. ethanol (C₂H₅OH)

3. propanol (C₃H₇OH)

4. butanol (C₄H₉OH)

what three properties do the first four alcohols share?

• flammable

• soluble

• can be oxidised to form carboxylic acids

why are alcohols often used as solvents in industry?

• they can dissolve things that water can’t

  • eg. hydrocarbons, lipid compounds (fats and oils)

• note: alcohols can also be used as fuels as they release lots of energy

what is the functional group for carboxylic acids?

-COOH

what is the general formula for carboxylic acids?

C_nH_2n+1COOH

how are carboxylic acids made?

by oxidising an alcohol (using an oxidising agent)

what are the names of the first four carboxylic acids?

1. methanoic acid (CH₃COOH)

2. ethanoic acid (C₂H₅COOH)

3. propanoic acid (C₃H₇COOH)

4. butanoic acid (C₄H₉COOH)

are carboxylic acids weak or strong acids?

• weak acids

  • don’t fully ionise

what do the negative ions formed by the (partial) ionisation of carboxylic acids end in?

-anoate

• eg. propanoic acid ⇌ propanoate ions + hydrogen ions

what is the symbol equation for the ionisation of ethanoic acid?

C₂H₅COOH ⇌ C₂H₅COO⁺ + H^-

• this is a reversible reaction

• the negative ion formed is ethanoate

what is formed when you react a carboxylic acid with a metal carbonate?

carboxylic acid + metal carbonate → salt + water + carbon dioxide

• carboxylic acids react like any other acid

what homologous group are used for addition polymerisation?

alkenes

what is the key feature of an alkene?

carbon-carbon double bond

• this makes alkenes unsaturated

what does the equation for an addition polymerisation look like?

• draw bonds of monomer directly above and below carbon-carbon double bonded atoms

  • simplify complex groups into their formula

• draw empty bonds of repeating unit going through brackets at sides

• remember ‘n’s - same number on both sides

how do you know the name of an addition polymer?

the name is poly(monomer)

• eg. poly(ethene), poly(butene), poly(chloroethene)

what conditions are required for addition polymerisation?

• high pressure

• catalyst present

condensation polymers can be made by joining together which two monomers?

• dicarboxylic acid monomers (contain 2 carboxylic acid groups)

• diol groups (contain 2 alcohol groups)

these are joined together by ester links

for every ‘n’ repeating units, how many water molecules are produced during condensation polymerisation?

2n

for molecules to be able to combine in condensation polymers, what two things must be true?

• each of the monomers must have at least two functional groups

• there must be at least two different functional groups overall

a small molecule is always given off during condensation polymerisation; what is this most often?

water

why are polyesters typically biodegradable?

microorganisms can break down the ester links

which type of polymerisation results in a non-biodegradable polymer?

addition polymerisation

what is the general formula of alkenes?

C_nH_2n

what is a dimer?

two monomers combined

when is a polymer referred to as a 'condensation' polymer?

when water is produced as a by-product of the reaction

what are polypeptide monomers called?

amino acids

what are dna monomers called?

nucleotides

what are carbohydrates made up of (monomers)?

sugars (monosaccharides)

what do polypeptides fold up, or combine, into?

proteins

which three functional groups are present in an amino acid (monomer)? which is not used for condensation reactions?

• amino group (left)

• carboxyl group (aka carboxylic acid group, right)

• R group (not used in condensation reactions)

what distinguishes different amino acids?

their ‘R’ group

what type of reaction combines amino acids into a polypeptide?

condensation polymerisation

what other names are there for a peptide bond, and where is this bond found?

• amide bond

• amide link

• between carbon and nitrogen in a polypeptide

how do we prevent the dna from getting damaged?

DNA is made up of 2 polymer chains that link together (naturally coiling around each other into a double helix shape)

what do all carbohydrates provide?

• energy

• refers to a number of different monomers and polymers

what are carbohydrate polymers called and what are some examples?

• polysaccharides

• eg. starch, cellulose, glycogen

what are carbohydrate monomers called and what are some examples?

• monosaccharides, aka sugars

• eg. glucose, fructose

what are most of the compounds in crude oil?

hydrocarbons (typically alkanes)

how are crude oils formed, and extracted from the ground?

• crude oil is formed naturally from the remains of dead plants/animals (especially plankton) millions of years ago

• the crude oil soaked into rocks and was stored

  • it can be removed by drilling into the rocks and extracting it

what is fractional distillation used for, in terms of crude oil?

• separating the different compounds within crude oil, by making use of their different boiling points

how does fractional distillation of crude oil work?

1. feed oil into a chamber - heat until gaseous

2. pass the gaseous mixture into a fractionating column (hot at the bottom, cooler going up)

3. the gas rises up the column, until it reaches a temperature below its boiling point, then condenses into a liquid

are smaller hydrocarbon chains more or less flammable and volatile than longer ones?

• more flammable

• more volatile

• lower boiling point (will condense higher up the fractionating column)

what are smaller hydrocarbon molecules most useful for?

fuels, as they are very flammable

what are large hydrocarbon molecules not useful for, and what can they be used for instead?

• not useful for fuels (not as flammable as smaller)

  • either used for another purpose

  • or broken down into smaller hydrocarbons, via cracking

what are petrochemicals?

A petrochemical is a substance made from crude oil, via chemical reactions

• eg. polymers, solvents, lubricants, detergents etc.

what is a feedstock?

a raw material used to provide reactants for an industrial reaction

what is are isomers?

• molecules with the same molecular formulas but different structural formulas

• made of the same atoms, but arranged differently

what is cracking?

breaking down long hydrocarbons into shorter, more flammable (so more useful) hydrocarbons

• this is a thermal decomposition reaction

what are the two types of cracking?

1. catalytic cracking

2. steam cracking

what are the steps for catalytic cracking?

1. heat (and vapourise) the long-chain hydrocarbon

2. pass hydrocarbon vapour over hot, powdered aluminium oxide (the catalyst)

3. as the long hydrocarbons come into contact with the catalyst, they split apart into two, smaller hydrocarbons

what are the steps for steam cracking?

1. heat (and vapourise) the long-chain hydrocarbon

2. mix with steam at very high temperatures

3. this causes the long hydrocarbon chains to split apart into two smaller ones

what is the word equation for cracking hydrocarbons?

long chain alkane → shorter alkane + alkene

• eg. decane → heptane and propene

• the number of hydrogens and carbons on both sides must be the same (balanced)

are alkenes saturated or unsaturated?

unsaturated

which are more reactive: alkanes or alkenes?

alkenes

what is the test for alkenes?

the bromine water test

• if added to a solution containing alkenes, bromine water will turn from orange to colourless

• this is because alkenes are very reactive so react with the bromine water (this would not happen with alkanes, and the water would remain orange)

what is the catalyst used in catalytic cracking of hydrocarbons?

hot, powdered aluminium oxide

what does an electrochemical cell do?

converts energy between chemical and electrical forms

• eg. fuel cells

what does a hydrogen-oxygen fuel cell do?

converts the chemical energy of hydrogen fuel and oxygen into electrical energy

• combines hydrogen and oxygen to form water, whilst creating lots of energy

what does a hydrogen-oxygen fuel cell look like?

1. central electrolyte (typically KOH - potassium hydroxide)

2. electrodes either side, connected by a wire

   • electrodes are made of porous carbon, and also contain a catalyst to speed up the reaction

3. anode and cathode compartments, with inlets (for hydrogen at anode and oxygen at cathode)

4. outlet for water and heat at the cathode compartment

how does a hydrogen-oxygen fuel cell work?

1. hydrogen enters and is oxidised by the anode

   • H₂ → 2H⁺ + 2e^-

2. electrons pass along the wire to the cathode, and hydrogen ions move through the electrolyte to the cathode

3. electrons and hydrogen ions react with incoming oxygen at the cathode, forming water

   • O₂ + 4H⁺ + 4e^-→ 2H₂O

4. water leaves the fuel cell via the outlet

how is electrical energy generated in a fuel cell?

• as the fuel enters the cell, it becomes oxidised

• this sets up a potential difference across the cell

• this causes electrons to move through the wire, across the circuit, generating electricity

what could hydrogen-oxygen fuel cells be used to replace in the future?

• replacing fossil fuel engines and batteries in vehicles (polluting)

  • hydrogen-oxygen fuel cells don’t produce any pollutants as waste products, last longer than batteries and are less polluting to dispose of

what are the pros of hydrogen-oxygen fuel cells?

• only require hydrogen and oxygen (both renewable, no fossil fuels)

• don’t produce carbon dioxide or other pollutants as waste products

• relatively simple devices

  • last longer than batteries

  • are less polluting to dispose of

what are the cons of hydrogen-oxygen fuel cells?

• hydrogen is gas - takes more storage space than fossil fuels or batteries

• hydrogen is explosive when mixed with air - dangerous to store

• making hydrogen fuel requires energy (often from fossil fuels)